1. Field of the Invention
The present invention relates to a method for manufacturing a thin film semiconductor device and a method for forming a resist pattern needed in the manufacturing of the thin film semiconductor device and more particularly to the method for manufacturing a thin film semiconductor device and the method for forming the resist pattern needed in the manufacturing of the thin film semiconductor device, whereby it is possible to achieve simplification of the manufacturing processes of the thin film semiconductor device and improving alignment accuracy during the manufacturing processes of the thin film semiconductor device.
The present application claims priority of Japanese Patent Application No. 2002-163083 filed on Jun. 4, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, in a method for manufacturing a thin film semiconductor device and for forming a resist pattern needed in the manufacturing of the thin film semiconductor device, an alignment process is impossible between a process of ion doping in which a pattern is not left on a substrate from which a photoresist (hereinafter may be referred simply to as a resist) has been removed and a subsequent process. Therefore, in such the case, an alignment pattern that has been formed in other processes is commonly used in the subsequent process.
Now, to explain a conventional technology, let it be assumed that, for example, as shown in FIG. 6A, an exposure mask 120 is used to form a light intercepting region 121, an alignment pattern region 122 serving as a light transmitting portion, and an ion doping region 123 on a surface of a resist layer 14.
Here, as shown in the same figure, on a surface of a transparent, insulating glass substrate 11 is formed an insulating film which is made of, for example, silicon dioxide as an underlying (undercoated) protecting film 12. On a surface of the underlying protecting film 12 is formed an underlying silicon layer 13 which is made of amorphous silicon (hereinafter referred simply to as “a-Si”). The resist lay 14 is coated on the underlying silicon layer 13.
After exposure and development operations have been performed in this state assumed above, as shown in FIG. 6B, in the alignment pattern region 122 and the ion doping region 123 other than the light intercepting region 121, the resist layer 14 has been removed by exposure and a resist layer 14(0) is now formed. That is, in the resist layer 14(0) are formed an alignment pattern portion 2 which forms space reaching an underlying silicon layer 13 and which corresponds to the alignment pattern region 122 shown in FIG. 6A, an ion doping portion 3 which forms space reaching the underlying silicon layer 13 and which corresponds to the ion doping region 123 shown in FIG. 6A and a light intercepting pattern portion 1 which corresponds to the light intercepting region 121.
If ion doping operations are performed in this state by using the resist layer 14(0) as a mask, since not only the ion doping portion 3 but also the underlying silicon layer 13 formed below the alignment pattern portion 2 are doped with ion at a same time, an exposed part of the alignment pattern portion 2 comes to have a same material as the ion doping portion 3. Then, when the resist layer 14(0) is removed to perform a subsequent process, optical discrimination between the alignment pattern portion 2 and the ion doping portion 3 becomes impossible and, therefore, an alignment mark cannot be identified.
Therefore, as shown in FIG. 6C, etching operations have to be performed by using not the resist layer 14(0) having a plurality of patterns as the mask but an etching mask 220 having only an alignment pattern region 222 that has been prepared separately. Thus, an alignment pattern 4 is formed on the underlying silicon layer 13 by an etching process. As a result, as shown in FIG. 6D, since the alignment pattern 4 is discriminated among other regions, in a subsequent process, this alignment pattern 4 can be used for positioning by using the resist layer 14(0) as the mask.
Moreover, in the process in which ion doping is first made, by preparing a mask to be used only for forming the alignment mark and by adding a process of forming a photoresist layer 14(0) using the prepared mask, a same state as shown in FIG. 6D can be obtained. That is, since, after the alignment mark has been formed, the process proceeds to a subsequent ion doping step, the photoresist layer 14(0) has to be formed separately and individually in two processes.
Thus, the conventional method for manufacturing the thin film semiconductor device and the conventional method of forming the resist pattern have problems not only in that, when a process such as ion doping has to be performed at a first stage, unnecessary processes are required which include a process of producing the alignment mark by separately preparing an etching mask or of performing main processing by preparing a mask to be used only for positioning with the alignment mark in a subsequent process but also in that indirect alignment for a subsequent process causes lowering in adjustment accuracy.